Abstract. This paper discusses the variation and validation of the precision,
or estimated random error, associated
with the ESA Level 2 products from the Michelson
Interferometer for Passive Atmospheric Sounding (MIPAS).

This quantity represents the propagation of the radiometric noise from
the spectra through the retrieval process into the
Level 2 profile values.
The noise itself varies with time, steadily rising between ice
decontamination events, but
the Level 2 precision has a greater variation due to the atmospheric
temperature which controls the total radiance received. Hence, for all
species, the precision varies latitudinally/seasonally with
temperature, with a small superimposed temporal structure determined by
the degree of ice contamination on the detectors.

The precision validation involves comparing two MIPAS retrievals at the
intersections of ascending/descending orbits. For 5 days per month of
full resolution MIPAS operation, the standard deviation of the
matching profile pairs is computed and compared with the precision
given in the MIPAS Level 2 data, except for NO2 since it has a large
diurnal variation between ascending/descending intersections.
Even taking into account the propagation of
the pressure-temperature retrieval errors into the VMR retrieval, the
standard deviation of the matching pairs is usually a factor 1–2
larger than the precision. This is thought to be due to effects such as
horizontal inhomogeneity of the atmosphere and instability of the retrieval.